The Clark level of invasion is a method developed by Wallace Clark for assessing the prognosis of melanoma by measuring how deeply the cancer has penetrated the skin's layers. This system classifies melanoma into five levels:- Level I: The melanoma is restricted to the outermost skin layer, known as the epidermis, and is also referred to as "melanoma in-situ."- Level II: The melanoma penetrates into the second skin layer, the dermis.- Levels III and IV: The melanoma extends further into the dermis but remains within the skin.- Level V: The melanoma reaches the fat beneath the dermis, penetrating into the third layer of the skin, the subcutis.The Clark levels help correlate the extent of melanoma penetration with the 5-year survival rate following surgical removal. The Breslow thickness measurement, introduced by Alexander Breslow, is now more commonly used. This method predicts 5-year survival based on the thickness of the invasive tumor. For instance, a melanoma less than 1.0 millimeter thick corresponds to a 97% 5-year survival rate, whereas a tumor thicker than 8.0 millimeters correlates with a 32% 5-year survival rate.